Helium embrittlement of Ti and P added austenitic alloys crept at 923 K

The helium embrittlement response of Ti and P modified and thermomechanically treated Fe–25% Ni–15% Cr type austenitic alloys was studied through post helium implantation creep testing. Helium was introduced into the specimen at 923 K with a concentration of about 60 appm by helium–3 ion irradiation with a cyclotron. Subsequent creep tests were carried out at the same temperature. In terms of creep rupture time, no significant degradation by helium was appreciated in the Ti added alloy, although the P modified one suffered from about a 40% reduction. On the other hand, a helium-related decrease in the rupture elongation was perceived in both alloys to a considerable extent. The beneficial result obtained from the Ti modified alloy suggests that the mechanical property deterioration induced by helium could be suppressed by proper Ti addition and/or microstructure controlling even in alloys with intermediate nickel contents (20–25%), like in Type 316 stainless steels of less nickel content.